Hard disc drives enable users of computer systems to store and retrieve vast amounts of data in a fast and efficient manner. In a typical disc drive, the data are magnetically stored on one or more discs which are rotated at a constant high speed and accessed by a rotary actuator assembly having a plurality of read/write heads that fly adjacent the surfaces of the discs.
The heads are suspended from flexure assemblies extending from arms of the rotary actuator assembly and include aerodynamic features that enable the heads to fly upon an air bearing established by air currents set in motion by the rotation of the discs. When the disc drive is deactivated, a shutdown operation is commenced wherein the heads are moved to a safe parking position before the discs come to a stop.
It is a continuing trend in the disc drive industry to provide disc drives with ever increasing data storage capacities using the same or a smaller form factor (i.e., outside dimensions) for the drives. As a result, successive generations of drives are often provided with discs that are closer together, reducing disc to actuator arm clearances. At the same time, disc drives are being utilized in environmentally harsher environments, such as portable computers, requiring increases in the robustness characteristics of the drives so as to withstand ever greater external vibrational and shock input levels. For example, a typical disc drive might be required to withstand up to a 200 g mechanical shock in a nonoperating mode.
Such mechanical shocks can cause significant deflection of the discs, leading to catastrophic damage to the disc media and heads. More particularly, disc to arm contact can induce a shock wave large enough to travel down to the flexure assemblies and heads, causing the heads to lift off of the disc surfaces as a result of the relatively flexible flexure assemblies to which the heads are attached. The heads can thus obtain significant velocities as they accelerate away from and then back toward the discs. When such velocities are sufficiently severe, damage can occur to the heads and the surfaces of the discs as the heads strike the landing zone portions of the discs. Moreover, should a head tilt during such liftoff, a corner of the head can strike the disc surface, increasing the probability of damage to the head or the disc.
Disc snubbers such as disclosed in U.S. Pat. No. 5,422,770 issued Jun. 6, 1995 to Alt ("Alt '770") have been provided in the prior art in an attempt to limit the deflection of the discs of a disc drive subjected to large nonoperational shocks. However, it has been observed that localized snubbers such as disclosed by Alt '770 tend to suppress disc deflection at the snubber location, but the remaining portions of the disc still typically deflect as before. This is particularly egregious when discs are fabricated from brittle materials, such as glass. Although glass discs are stiffer and possess harder surfaces than discs fabricated from aluminum, so that glass discs tend to deflect less than aluminum discs, glass discs are more likely to shatter when subjected to high amplitude mechanical shocks.
Accordingly, there is a need for an improved approach to minimizing damage to a disc drive as a result of nonoperational shock by limiting the ability of the discs to contact the arms of an actuator of the disc drive.